Electric rivet heater



Feb. 7, 1928.

. 1,658,259 J. E. $EDERHOLM ELECTRIC RIVET HEATER Filed Dec. 8. 1924 6 Sheets-Sheet 1 [71/671, 2 3 Jam/f. JEDE/Pf/OLM 5/ CPGAKQJWW r77- TOR'NE Y5 Feb. 7, 1928.

. 1,658,259 J. E. SEDERHOLM ELECTRIC RIVET HEATER Filed Dec. 8. 1924 //6 6 Sheets-Sheet 2 Feb. 7, 1928.

J. E. S E DERHOLM ELECTRIC R'IVET HEATER F'led e0. 8. 1924 6 Sheets-Sheet 3 Int 7 JED/1 125 Jame 104M Gav-Q, WWW

Feb. 7, 1928. 1,658,259

J. E. SEDERHOLM ELECTRIC RIVET HEATER Filed De 8. 1924 6 Sheets-Sheet 4 5 WQ WW A r-roexvsy's Feb. 7, 1928. 1,658,259

J. E. SEDERHOLM ELECTRIC RIVET HEATER Filed Dec. 8. 1924 6 Sheets-Sheet 5 32 E [ll/672L492" 32 .[Of/A/ZJEOEQf/OLM Feb- 7,

J. E. $EDERHOLM ELECTRIC RIVET HEATER Fil'ed Dec. 1924 6' Sheets-Sheet 5 lTroRA/E Y6 Patented Feb 7, 1928,

UNITED STATES 1,658,259 PATENT OFFICE.

JOHN E. SEDERHOLM, OF ST. FAUL, MINNESOTA, ASSIGNOR TO AMERICAN HOIST & DERRICK COMPANY, OF ST. PAUL, MINNESOTA, A CORPORATION OF MINNESOTA.

ELECTRIC RIVET HEATER.

Application filed December 8, 1924. Serial No. 754,613.

This invention relates to new and useful improvements in electric rivet heaters particularly designed for use in heating rivets to be used in hot-riveting structural steel frames for buildings, bridges, etc, and more particularlyrelates to such heaters adapted for heating rivets for use in the construction of steel boilers wherein the seams and joints must be securely riveted in order that the boiler, when completed, will be leak-proof and safe.

Rivet heaters in use at the present time are usually so constructed as to direct a uniform flow of current through the entire length of the rivet when heating it. By thus causing a uniform flow of current to fiow through the rivet the small end of the rivet is usually heated to a higher temperature than the opposite or head end thereof caused by the current carrying capacity of the small eiid of the rivet being relatively less than the head. and thereby offering a greater resistance to the flow of current therethrough. The above condition may also be intensified as result of the possibility of obtaining a relatively poorer electrical connection between the small end of the rivet and the heating element, than may be obtained be tween the head end and its respective heating element, caused by the smaller end of the rivet sometimes being very rough and uneven, thereby making only a point contact with the heating element. Such heating of the rivet has been found unsatisfactory and objectionable in certain classes of work, such, for instance as boiler making, where it is essential that all joints and seams be made steam and water tight. In the manufacture of steam boilers, the method most commonly employed atpresent to render the boilers leak-proof, is to peen over the edges of the rivet heads with an air hammer or other device after the rivets have been headed over, thereby substantially uniting the edges of the rivet heads with the boiler plate. with the result that a leak-proof joint will be obtained between the rivet and boiler plate. The above procedure is usually necessary as a result ofthe fact that the body or grip of the rivet usually cools quicker than the end thereof which is to be headed over, caused by contacting with the cold walls of the rivet hole. Therefore when the end of the rivet is headed over a head will be formed thereon before the body or able as it requires considerable labor with a resultant increase in the cost of manufacture.

An object of the present invention is to provide an improved rivet heater so constructedand designed as to enable the operator to heat the body of the rivet forming the grip, to a relatively higher temperature than the end thereofwhich is to be headed over. By thus heating the body, or that portion of the rivet which passes through the plates and forms the grip, to a very high degree of temperature, and the small end thereof to a considerably lower temperature, the body or grip portion of the rivet will expand and completely fill the rivet hole as soon as pressure is brought to bear against the end of the rivet in heading it over. Such expansion of the rivet body will occur substantially before the head begins to form on the end of the rivet with the result that a leak-proof joint will be provided between the body of the rivet, and the walls of the aperture in which it is seated, thereby eliminating the necessity of having to peen over the rivet heads after the boiler has been riveted. The above method of riveting will alsogreatly increase the strength of the riveted joint as the two members or plates will be firmly and securely held together, thereby eliminating all danger of the plates creep ing or changing their relative position, which is a well known occurrence when employing the present method of riveting wherein the entire rivet is heated by directing a uniform flow of current therethrough. The above difficulty is usually caused by some of the rivets being loose as a result of the rivet bodies not expanding sufliciently to completely fill the apertures in which they are seated before the heads are formed on the ends thereof. Further, the rivet heater g v V 1,658,259

is provided with means whereby the operator'may conveniently vary the temperature at either end of the rivet as required, or if desired, only one end of the rivet may be heated. The apparatus is also readily adjustable to all sizes of standard rivets.

Another object of the invention, therefore,

is to provide an improved rivet heater of simple construction which is capable of being operated to full capacity continuously and will be efficient and positive in per-' from the following description and the accompanying drawings and will be pointed out in the annexed claims.

In the accompanying drawings therehas been disclosed a structure designed to carry out the various objects of the invention but it is to be understood that the invention is not confined to the exact features shown as various changes may be 'made within the scope of the claims which follow.

' In the accompanying drawings forming part of this specification,

Figure 1 is a view in front elevation of the improved rivet heater showing a rivet positioned between the movable contacts thereof;

Figure 2 is a side view of Figure 1;

Figure 3 is a sectional view on the line 3-'3 of Figure 1 showing the novel construction of the secondary elements;

Figure 4c is a sectional? view on the line H of Figure 8 showing the relative positions on the laminated core of the primary windings and secondary elements;

Figure 5 is a plan view of the apparatus showing the various controls;

Figure 6 is a sectional view on the line 6+6 of Figure 8 with the operating levers and foot pedalsomitted, showing the preferred manner of mounting the horizontal contact blocks on the secondary elements;

Figure 7 is a wiring diagram of the apparatus showing the magnetic circuits generated in the iron core when the primary windings or coils are energized;

Figure 8 is a diagrammatic view showing the primary windings and secondary elements mounted on the magnetic core and also indicating the path of the induced current built up in the secondary elements when the primary windings are energized and a rivet is interposed between the contacts thereof, and y 7 Figure 9 is an enlarged view showing a rivet positioned to be headed over, the shaded port-ion indicating the grip of the rivet and the portion which is heated to the highest temperature; a rivet also being shown after having been headed over to show how the grip of the'rivet will completely fill the rivet hole.

The novel rivet heater shown in the accompanying drawings is an improvement on the form of rivet heater shown in my pending application Serial #579,940, filedAugust 5, 1922. As here shown, the-frame of this rivet heater preferably comprises the upright front legs 11 and similarly shaped rear legs 12 connected together at their bottoms by means of the cross members 13. Plates 14 and 15 are secured to the front and rear legs as shown in Figures 1, 2, 3 and 4, which plates function to securelyconnect the legs together, thereby providing a very rigid and substantial frame.

A magnetic core, preferably rectangular in shape and constructed of laminated sheet metal in the usual manner, is mounted in the upper portion of the frame and is securely clamped between the front and rear legs "by means of tie bolts 16. As shown in Figure 5, the front and rear legs 11 and 12 are preferably of angle iron construction sothat the ends of the magnetic core may be clamped between the rightangled walls thereof, thereby providing a very rigid support for the core. As shown in Figure 4-, the magnetic core preferably comprises the upper and lower horizontal sections 17 and 18 and an intermediately= disposed section 19 preferably of larger cross section connected together at their ends by means of the upright sections 21. The upper and lower parallel longitudinal cxtending members of the magnetic core are provided with suitable primary windings or coils 22 and 2", respectively, as shown.

These coils are preferably mounted adjacent each end of the core and are suitably insulated therefrom as is customary in crevices of this kind. netic core and the arrangement of the primary windings or coils thereon is such that when the coils are energized two distinct magnetic circuits will be built up in the magnetic core as indicated by the arrows in the wiring diagram. Figure 7.

An important feature of this invention resides in the novel construction of the sec ondary elements which are mounted in spaced parallel relation on the magnetic core The construction of the magand'suitably insulated tierefrom. As shown in Figure 3, Q2101 secondary element is preferably con ucted of two members which will here :er be referred to the outer fliU neeaeae and the inner secondary element. As the two secondary elements and the movable contacts mounted thereon are similar in construction, it will be necessary LO describe but one of the secondary elements, and its associated parts, like parts being referred to by like numerals. The outer secondary element preferably comprises the upper and lower horizontal legs or portions 2%- and 25, connected together at the rear of the machine by means of the upright portion The upper leg 2st is preferably provided with an elongated head 27 which functions to provide a contact face or surface 28 for a sliding contact block 29 mounted thereon. Yieldable means are preferably provided for securing the contact block 29 in electrical contact with the contact face 28 of the secondary element. Such means preferably comprises a pair of studs 30 which are secured to the head 27 of the element and out wardly project therefrom in spaced parallel relation through an elongated opening 31 provided in the block, and having a wheeled carriage 32 mounted thereon which is yieldably held against the outer face of the contact block by means of suitable compression springs 33 and the nuts received in threaded engagement on the ends of the studs 80. The contact block 29 is also preferably provided with a longitudinal flange 35 on each side which functions to retain the contact block in true alignment with the head 27 when moved thereon. By means of the yieldably mounted carriage 32 it will be seen that the contact block 29 will be held in direct contact with the face 28 of the head 27 of the secondary element, thereby providing a good electrical contact at all times regardless of the position of the block thereon.

The inner secondary element 36 is pr r ably U-shaped in form and comprises the upper and lower spaced parallel l gs 3'" and 38. In the particular construction her shown the lower legs 25 and 38 of the outer and inner secondary elements, respectiyely, are secured together, the two elements preferably being formed of an integral casting as shown but with the inner elementconnected with the lower leg of the outer elcment only at its front portion. Fig. 8.) Thus a common return circuit is pro- Vided for the two elements corresponding to the common return provided by the intermediate member 19 of the core. The inner and outer secondary elements are insulated from one another at all other points, (see Figs. 3 and 8) an air gap being formed by sawing. It will be noted that the U-shaped members have a nested relation and that the two lower legs of the inner and outer elements are disposed at the outer side of the core while the two upper legs respectively pass between the intermediate section 19 a ing ell-acts are additive for, in the case, super-heating the grip portion of the rivet.

By this novel co struction, the lower legs 25 and of the two members will provide a continuous contact face 39 adapted to receive a similar contact block 41 inoyably mounted thereon ZillL yieldubly held in electrical contr t therewith by means of a carriage similar in construction to the one shown in con nection with the upper contact block 29 d lam wn h will, therel'ore, be referred to by like a 1n er-a l and 6, it will be L horizontal leg of inner or smaller secondary element 35 orovided with a head d2 upon which a 1 smaller contact block 43 is mou The means provided for securing the at block to the head similar to hown with reference to the upper and contact blocks it) and ell and will "re be indicated b like numerals. A ary contact nember ll, preferplurality contact faces ll), non the head l2 and is secured thereto by spring -l.-? and a nut 28, secured to the head as member ll cooperate l; to provide a dual tne rivet when interposed thereas shown on the l .ft-hand side of l and and it a 0 functions as an the rivet en the movable is meted into electrical contact with I clearly shown in Figure 1. By ans of the pirotal mounting of the conct member dd and its plurality of contact aces 425, the member may be rotated to present a clean contact the rivet. should the contact being used become ineffective as a result of being pitted or worn from areing. etc.

s are provided whereby the upper oi. c ocks 29 may be conveniently actuated as when it is desired to position a 'et between the upper and lower contact l for heating. Each contact block l3 rably has a forked bracket secured the upper end thereof to which the upper e actuating bars 51 are pivotally connected to suitable operating pedals 52 pivchine. The springs 55 function to yieldably retain the foot pedals 52 in their raised position thereby tending to downwardly force the upper contact blocks 29 into contact with the rivets when interposed between these bloc and the lower contact blocks 41. When it is desired to inte-rpose a rivet between the contact blocks 29 and 41, the

v upper contact block 29 will be raised by the All operator downwardly moving the foot pedal connected thereto. As soon as pressure is released from the foot pedal, tne upper block 29 will be downwardly moved into electrical contact with the rivet thereby closing the heating circuit which will hereinafter be described. The lower contact blocks ll are provided with means whereby they may readily be adjusted to the proper position which is usually determined by the thickne'ss of the elements to be riveted together or by the length of the grip portion of the rivet. The means provided for thus adjusting the positions of the lower contact blocks 41 preferably consists in the provision of suitable hand levers 57 which are preferably mounted on studs 58 provided on the lower horizontal leg portions 25 of the outer secondary elements as shown in Figures 2 and. 3. Each lever is connected with its respective contact block by means of a link 59 having one end pivotally connected to the lever and the other similarly connected to the side of the contact block. The levers 57 are also provided with suitable latches 61 adapted to engage quadrants 62 mounted on the angle bar 56 of the frame, whereby the blocks may be conveniently and adjustably held in ad justed position.

The means provided for actuating the relatively smaller horizontally mounted contact blocks preferably consists in the provision of a pair of opposed arms 63 which are pivotally mounted on the frame of the apparatus by means of pivots or bolts 64:. These arms are connected to their respective contact blocks by means of brackets 65, as shown in Figures 1 and 6, so that when the arms are oscillated, the contact bloc-ks will be actuated. An anti-friction roller 66 is referabl Y mounted in the uaaer forked.

end portion 67 of each arm 63 and these rollers are adapted to" be engaged by suitable cams 68 mounted on the adjacent sides of the upper contact blocks 29. Each arm 63 is yieldably held in contact with the cam 68 by means of a spring 69 having one end will subsequently be described.

upper contact block 29 is lowered to the position on tl e left-hand side of the above iigure, the horizontal contact block d3 will simultaneously be moved into contact with the rivet by the action of the spring, thereby completing the two heating circuits which The oscillating arms 63 are preferably insulated from the machine frame. A convenientform of insulating the arms from the frame is shown in Figure 2 wherein each arm is constructed of an upper and lower section having an insulating block 71 interposed therebetwcen; It is to be understood, of course, that one f the sect-ionswill be insulated from the bolts 72 by such means as suitable insulating bushings and washers ,(not shown), mounted on the bolts so that current cannot pass from one section tothe other through the bolts 72. I Y

Means are also provided whereby the horizontally mounted contact blocks 4E3 may be manually actuated should it be desired to obtain a better contact with the rivet. Such means preferably consists in pivot ally mounting a hand lever 73 over each contact block 48. These levers are mounted on suitable pins 74 secured to the heads d2 of the upper horizontal leg 37 of the inner secondary elements 36. A pin 75 is mounted in each contact block eifiand these pins upwardly extend therefrom through elongated apertures provided in the hand levers 78. Thus it will be seen that when the hand levers 73 are outwardly moved from the position shown on on the right hand side'of the figure, the contact block 43 on the righthand side of the figure will be outwardly moved to the position shown in Figure 1 so that a rivet may be interposed between the upper and lower contact blocks 29 and 41, respectively.

The wiring diagram of this novel rivet heater is shown in Figure 7. the primary coils 22 and 23 are connected up insuch a manner that a number of different heats maybe obtained, and also that the entire length of the rivet may be heated to a substantially uniform temperature, or one end may be heated to a considerably higher temperature than the opposite. Such heating of the rivet is accomplished by the simple manipulation of suitable control switches provided for that purpose. Elec- As here shown nessgaee' trical energy is supplied to the primary coils 22 and by means of conductors 77 and T8 through a main line switch 79. The conductor 77 leads from the binding post 81 of the main line switch 79 to a terminal 82 on the upper primary coil 22 on the right hand side of Figure T. The other primary coil is connected to the conductor 77 by a wire 83. The lower primary coils 338 are similarly connected to the conductor 77 by means ot wires 8% and 85. Thus it will be seen that one end of each of the primary coils will always be in electrical connection with the binding post 81 of the main line switch. The

' conductor 78 of the other side of the line connect-s the binding post 86 of themain line switch with the high heat post of a suitable heatcontrol switch mechanism. As shown in Figure 7, this control switch mechanism preferably comprises a plurality of interlocking switches, preferably three, thereby providing a low heat switch 88, a medium ieat switch 89 and a high heat switch 91. These switches are also indicated in Figure 1 and on the. wiring diagram by the letters L, M, and H, representing the low, medium and high heats. These switches are electrically connected to the conductor 78 as shown. The low heat switch 88 is connected to the-low heat terminals of the lower primary coils by means of wires 93 and 91, the medium heat switch 89 is similarly connected to the medium heat terminals 95 of the lower coils by the wires 96 and 97; and the high heat switch 91 is connected to the high heat terminals 98 ot the lower primary coils 23 by means of the wires 99 and 101. Thus it will be seen that by the provision of the control switches 88, 89 and 91, a number of different heats may be obtained. These switches control the flow of current through the inner or smaller secondary elements and therefore through the body or p of the rivet as indicated by the arrows in Figure 8. The interlocking heat control switches shown in the wiring diagram, Figure 7, and also shown in Figure 1, are similar in construction to a control switch forming the sul ject matter of my pending application, Serial #729,807, filed r rugust 2, 192

1L similar heat control switch mechanism is provided for controlling the amperage flow through the upper primary coils This switch is preferably provided with a similar number of control switches 103,101, and 105 which are in electrical connection with the main line conductor 78 a. l The low heat switch 103 is conneca low heat terminals 106 of the upper 13 coils 22 by wires and 108. the switch to the medium heat terminals 109 coils by the w res 111 and 112, and the 105 to the high heat terminals or. t e primary coils by means of the wires 11- and 115. By the provision oi the heat control switches 103, 104 and 105 the flow of current in the upper primary coils 22 may be controlled, as desired, which in turn controls the flow of induced current in the larger or outer secondary elements, as indicated by the arrows in Figure 8. The wiring diagram shown in Figure 7 is arranged tor a 220 volt, cycle alternating current circuit, but it is to be understood, of course, that the primary coils may be connected in such a manner that the apparatus may be used for diii'e-rent voltages, such for instance, as 4&0 volts.

The operation of this novel rivet heater may be explained with reference to Figures 1, T and 8. Before placing any rivets between the contact blocks for heating, the main line switch 79 will be closed as shown in Figure '7, thereby electrically connecting one end of each primary coil with the main line conductor 77. One of the heat control switches of each pair'ot primary coils will then be closed as shown in this figure, thereby completing a circuit through each pair of coils. in Figure 7, the high heat control switch 105 controlling the flow of current through the upper primary coils 22 is shown in circuit-closing position, while the circuit through the lower primary coils 23 is shown completed by the closing of the low heat switch 88. When the switches have been closed, as above described, the circuit through the upper primary coils will be as follows: from the main line switch 79 through the conductor 77, to the end terminal 82 of the primary coil on the right-hand side of Figure 7, through a portion of the winding of the coil to the high heat terminal 113, thence through the wires 115 and 114 through the switch 105, conductor 78, and back to the main switch terminal 86, thereby completing the circuit. The other primary coil 22 will also be energized as a result of having one end thereof connected to the conductor 77 by the wire 88 while the high heat; terminal 113 thereof is connected to the wire 114 leading to the switch 105. The lower circuit will be as follows: From the conductor 7'7, the current will flow through the wires 81- and 85 to one end of each of the lower nary coils 23, thence through all of the urns of each coil to the low heat terminal osts 02,

heat eontrtl switch 88, and back to conduct-or leading to the main line ch 79. H ion the main line switch 7 9 and the two control switches are closed as above desc ibed all of the primary coils will be ener- ,t 'ed which will cause magnetic lines of torce to flow through the sections of the agn *ic core, as indicated by the dotted mes Figure 7. As a result of the novel L 'gementot' the primary coils on the acne: and lower sections 17 and 18 of the through the wires 94; and 93 to the magnetic core, two complete magnetic circuits will be generated in the core. The two magnetic circuits flowing through the magnetic core will cause an induced current to be built up in each of the secondary elements as is indicated by the arrows in Figure 8.

'On the left hand side of this figure, it will be notedthat a rivet has been positioned betweenthe upper and lower contact blocks as indicated by the arrows.

29, and 41. This rivet functions to complete the circuit through the secondary elements, Referring to this figure itwill be seen that the current flowing through the outer secondary elements, (which current is induced by the upper magnetic circuit shown in Figure 7),

will flow from the upper horizontal leg 24 of the secondary element through the contact block 29, through the rivet, lower contact block 41, the lower horizontal leg 25, and through theupright portion 26 of the outer secondary element and back to the horizontal ally becomes the hottest, as a result of the possibility of a poorer contact being obtained between the end of the rivet and the contact block 29 than is obtained at the other end of the rivet, thereby causing greater resistance to the flow of current through that end of the rivet. It is, therefore, desirable that means be provided whereby the body or grip ortion of the rivet may be heated to an equal or relatively higher temperature than the smallend, thereof in order that the body or grip of the rivet will expand sufficiently, when headed over, to completely fill the rivet hole in which it is seated. Heating the lower or body portion of the rivet to a higher temperature as above stated is'readily accomplished by means of the lower primary windings 23. When the low heat switch 88 is closed as above described, an induced current will be built up in the inner secondary elements 36 and when the horizontally mounted contact block 43 is moved into contact with the body of the rivet. which willalso be in contact with one of the contact members 45, a complete circuit will be formed which will be as follows: through the upper horizontal leg 37 of the secondary element 36, through the lower half of the rivet, contact block 41, lower horizontal leg 38 of the inner secondary element and back to the upper leg 37. By the closing of the above circuit, the flow of current through the lower portion or body of the rivet will be neaaaae:

substantially increased, thereby causing that portion of the rivet to be heated-to a much higher temperature than the upper end thereof. 7 r

In Figure 9, there is shown a rivet insert.- ed in an aperture before being headed over. The shaded portion of the rivet here shown indicates the grip or body portion of the rivet which has been heated to a relatively higher degree of temperature than the upper end thereof. Thus when the upper end of the rivet has been headed over, as shown on the right-hand side of the figure, the body or grip portion thereof will be expanded sufliciently to completely fill the rivet hole, thereby positively preventing any leakage around the body of the rivet and also providing a very rigid and rugged connection between the two plates or members to be riveted together. Vvhen the plates have been riveted together as above described, the body or grip of the rivet will be substantially united with the walls of the aperture in which the rivet is mounted when a head is formed on the end thereof, caused by the expansion of the rivet body as a result of bein heated to a relativel hi her de ree D b O of temperature than the small end thereof.

From the foregoing therefore, it will readily be seenthat by the provision of the two interlocking heat control switch mechanisms, one preferably being provided for the uppeinand one for the lower primary coils, it will be possible to heat the body or grip portion of the rivet to a relatively higher temperature than the small end thereof. It will also be possible to heat the small end of the rivet to a higher degree of temperature than the body or grip portion thereof by decreasing the number of ampere turns of the lower primary coils. 23 and by increasing thenumber of ampere turns of the upper primary coils Such increasing and decreasing of the number of ampere turns of the primary coils is effected by the 7 opening and closing of the heat control SWitCllcS as above described. It is also to be understood that, if deslred, either the upper or lower primary coils may be cut.

out of the circuit thereby causing only one set of contact blocks to function; that is, if the lower coils 23 are eliminated from the circuit, then current will be induced in the outer secondary elements only, while if the upper primary coils 22 are eliminated from the circuit, then the current will flow through the inner secondary elements 36 and through the lower portion of the rivet only, thereby heating only a portion of the rivet. V V

In Figure 1, the main line switch 79 is shown mounted on the left-hand side of the frame of the apparatus, while the heat control switches are shown mounted one on iii) (ill

masses" A lifting bail 116 may be provided on the frame whereby the apparatus may readily be lifted from one place to another by a suitable lifting means. The construction of the novel secondary elements, as shown in Figure 3, may be varied from the particular construction shown. As here shown, it will be noted that the lower horizontal legs of each pair oft secondary elements are united by being integrally formed in the molding ot the two elements, which are preferably constructed or copper or other suitable conductive material. When constructed as here shown the upper portion of the inner secondary elements may be supported by the horizontal portion 26 of the outer secondary elements by such means as the straps 117, which have their ends suitably bolted to the two secondary elements as shown in Figure When such straps are used it is necessary that one end thereof be insulated from one of the secondary elements in order that there be no leakage of current from one secondary element to the other. If desired, the secondary elements may also be independently constructed and mounted in their respecti positions on the magnetic core, it being understood that the lower horizontal legs thereof need not be electrically connected together as shown in the drawings. The purpose of constructing the secondary elements with their low horizontal legs united, as shown, is to provide means whereby the contact faces against which the contact blocks are mounted may be convenienly machined so that th y will be in true alignment. It the secondary elements are independently con structed it will be necessary that they be rigidly secured together in order hat a good electrical connection may be obtained etween the contact faces thereof and the contact blocks.

in Figure 8, the induced current llow through the secondary elements is shown as flowing in one direct-ion but it is to be understood, of course, that when. using alternating current the flow of current rough these elements will alternately flow .lCCtlOIlS which is a well-known l'ic oi alternating current flow.

The rivet heater shown in the accompanydrawings employs two upper and two grimary coils but it is to be under- 7 that one or more of such coils may be it desired without departing from the claim adapted to engage a rivet at 1ntern1ehate omt, a pivoted lever connections beeen the lever and o..e member of said 'econd pair of holding members, a s or normally drawing the i "t mentioned pair of he illll members, nd a cam upon one or the first mentioned embers adapted to throw said lever to move said second member to non-clamping position when the first member travels to a similar position.

2. An appa 'atus oi the class described, comprising primary coils having an electric ci cult, secondary elements associated with the coils, through which separate induced currents are established by the primary coils, one of the said secondary element having movable contacts for ends of a rivet to be heated, with therivc completing the circuit, the other secondary element having movable contacts for engaging the shank ol the rivet intermediate its ends, a cam and lever mechanism within the control of the o1 erator for actuating said contacts to advance the same to rivetcontact and clamping positions, and e trical connections for the coils for ener ic ing and controlling the same for generating a separate cur-renti or each secondary element.

3, An apparatus of the described comprising primary coils having an electric Circuit, secondary elem nts tl'n'ough which separateinduced current: are c: the primary coils, one of said secondai inents having movable contacts for the shanl: of a rivet or worl; diate its ends, and mani'ially operable anisin tor sinniltanci'msly actuating contacts for en the rivet to CO1;

i. A device ot the class d arising a nni 'n ic core rber. .f coils indu.

said mg, holding and causing iete both cn'cuits.

' ribed therein, g upper vith the core, an inner also having upper am. 10 ments mounted upon and i core and substantially in another, said core and co' duce a separate current in I the currents uni-direction trically connectingand lower legs of said ment and the lower leg cary element, said ri an intermediate noint wit said inner second ry e "he c. cvice to pass the currents in th that portion of oerhe tec.

magnetic core havin masses.

- for engaging opposite ends of a rivetto hold the rivet as a circuit making member, an inner secondary element also having upper and lower spaced legs lying within, and aligned with said first mentioned legs, one passing between the intermediate and outer parallel members, and the other adjacent and outside of the same outer parallel member, adjust-able contacts upon the upper inner leg, adapted to electrically engage the rivet at an intermediate point, and electrical connections for energizing and controlling the coils tor simultaneously gencrating heating currents and causing the same to pass through both secondary elements, and through a rivet in the same direction, whereby one part of the rivet is superheated by the additive effects 01" two distinct and separately induced currents.

6. A magneticcore having parallel members, primary coils arranged upon said parallel members, outer and innersecondary elements, each having upper and lower legs, respectively passing between, and lying at the outside of, said parallel members at right angles thereto, insulated therefrom and substantially insulated from one another, the upper leg of the outer member and the lower legs of the inner and outer members having cooperable adjustable contacts 'tor'holding a rivet,'and the upper inner leg of the secondary member having adjustable cooperable contacts adapted to engage a rivet at an intermediate point, and electrical connections for energizing and controlling the coil for simultaneously generating separate currents, one in. each secondary element, passing the same through the rivet with the currents flowing in the same direction whereby a portion of the rivet is superheated.

7. An apparatus of the class described comprising a magnetic core having parallel members, coils upon the members adapted to generate two currents therein, outer and inner secondary elements on said magnetic core, each adapted to receive one of the currents induced by the core, each secondary element having upper and lower spaced legs, movable contact blocks mounted upon the legs or" said secondary elements adaptedto clamp a rivet to be heated, and anti-friction means secured to said legs and adapted to yieldably hold said contact blocks in electri-- cal contact with said legs.

8. An apparatus of the class described comprising magnetic core having parallel members, outer and inner secondary elements on said magnetic core, each having upper and lower spaced legs, two sets of clamping contact members adjustable on the legs, the sets an ularly related, the first for engaging ends 01 a rivet and the second for engaging a rivet laterally at an intermediate point, a pivoted lever, connections between the lever 01" the last mentioned contact member for translating the same, means for yieldably urging the lever in, contact direction, a cam upon one of the first mentioned contact members adapted to engage and swing the lever when moving to non-clamping position, for simultaneously correspondingly moving the lever-connected memberand treadle means for translating the cam carrying member. 7 9. A clamping and contact device of the class described including a first pair of aligned clamping and contact members, a second pair of similarly related clamping contact members, a pivoted lever connected, with a contact member of the first pair, a spring for urging the lever in clamping and contact direction, a cam onfone member of said secondary pair of contact members, said lever engageable by the cam when moving from clamping position, whereby after one member moves to clamping position the lever acts to simultaneously move the other to and maintain it in a similar position,

10. A magnetic core having parallel members, secondary elements traversing said core at right angles thereto and insulated therefrom, providing upper lower, and intermediate'legs, and contact devices one upon each upper and lower leg adjustable for engaging opposite ends of a rivet, clamping and contact devices upon said intermediate leg adjustable to engage a rivet at an interme diate point, and primary coils upon said core arranged connected and electrically controllable, and adapted to induce two distinct heating" currents in the secondary elements, with the secondary currents uni-directional. I

11. In a device of the class described, a magnetic core having three parallel members connected together at opposite ends, two U-shaped secondary elements, outer and inner, arranged in nested relation, each providing upper and lower legs, one leg of the outer member disposed between, crosswise and insulated from two of the parallel members of the core, and the other extending end of the otherelement, clamping elements upon the projecting ends of the elements adapted respectively to contact a rivet at its ends and at an intermediate portion, coils upon the core, and electrical means for energizing the coils to pass a separate current through each secondary element, with the current uni-directional, through a rivet clamped completing the circuit therebetween.

12. A work clamping device for an electric riveting-heating machine, comprising a first pair of aligned contact and rivetingholding members slidably adjustable, a second pair of contact and rivet-holding members slidably adjustable and adapted to engage a rivet at a point intermediate its ends, a pivoted lever, a link connecting said lever with one of said members, a spring for normally drawing the lever toward the first mentioned members and a cam upon one member of the first mentioned pair of members adapted to engage and retract the lever when the members are retracted from clamping position, and further adapted to release the lever to obtain clamping action of the other member when the first-mentioned members travel to clamping position.

13. A device of the class described comprising a magnetic core having parallel members, primary coils arranged on said parallel members, electrical means for con trolling the coils for developing two currents in the core, the currents having a common return in the same direction in the core, an outer secondary element having upper and lower legs, an inner secondary element having upper and lower legs, said elements mounted upon and insulated from the core and substantially from one another, and each arranged and adapted for receiving a separate current induced by the core with the currents uni-directional, and having a common return through the lower elements, and a rivet electrically connecting at its ends the upper and lower legs of said outer secondary element and the lower leg of the inner secondary element, the upper leg of the inner secondary element connected with,

and adapted to pass a second current through the rivet from an intermediate portion, to superheatthat part of the rivet through which both uni-directional currents pass.

14. A device of the class described, comprising a magnetic core frame providing three parallel members spaced and connected at their ends with the intermediate member as a common return for a current set up by the core, outer and inner U-shaped secondary elements disposed one within the other and mounted upon the core crosswise thereof, having corresponding legs at the outer side of the core connected to provide a common current return, with the other legs of the inner and outer element respectively passing between the intermediate member and different outer members, coils upon the outer members of the core arranged for generating currents having the same direction in the common return or intermediate member, clamping means upon the outermost legs of the secondary elements for holding a rivet in position for passing a current lengthwise therethrough, and means upon the central or innermost leg of the inner secondary member for making electrical contact with the rivet at an intermediate point, whereby separate currents are induced in each secondary element with the current flowing in the same direction for obtaining additive heating effects through a portion of a rivet for superheating that portion.

15. A magnetic core having parallel members, secondary elements traversing said core at right angles thereto and insulated therefrom and providing upper, lower and intermediate legs, and primary coils upon said core arranged and connected and electrically controllable and adapted to induce two dis tinct heating currents in the secondary elements, with the secondary currents uni-directional.

In witness whereof, I have hereunto set my hand this 1st day of December, 1924.

JOHN E. SEDERHOLM. 

